Monday, April 5, 2010
Two papers involving researchers at The University of Texas at Austin were prime examples of the scientific process in action.
One paper, published in Science, reconfirmed that a giant asteroid striking the Earth at the Yucatan Peninsula was responsible for wiping out dinosaurs—and a lot of other creatures—65 million years ago. The other paper, published in the Journal of Human Evolution, overturned highly publicized claims made about the Darwinius masillae fossil, which said it was the oldest human ancestor.
In this post, we’ll talk about how the process worked with the dinosaur extinction with Sean Gulick and Gail Christeson, researchers at the university’s Institute for Geophysics. They were part of the 41-member team that reviewed the science about the extinction event.
The background: Thirty years ago, Walter Alvarez, Jan Smit and their coworkers (who included Walter’s father Luis, a Nobel Prize physicist) suggested that a large meteorite slammed into Earth 65 million years ago and caused one of the most severe mass extinctions in Earth’s history, ending the age of the dinosaurs. This extinction is known at the K-Pg boundary.
In 1991, an impact crater more than 200-kilometers-wide that coincided with the extinctions was discovered in Yucatan, Mexico. Since then, the impact hypothesis has gained overwhelming acceptance within the scientific community.
Since then a small number of scientists have suggested that the Chicxulub (”chik-shoo-loob”) impact in Mexico happened 300,000 years before the K-Pg boundary, and therefore, came too early to have been the major cause of extinctions.The recently published paper, Gulick said, “summarized the abundance of scientific evidence on the timing and effect of the impact to conclude that the majority was correct and that the rather vocal minority’s evidence does not withstand scientific scrutiny.” Christeson said the paper came about because a group of scientists was continually frustrated by press reports that made it seem like there was a controversy.
“The vast majority of the scientific community was convinced of the link between the Chicxulub impact and the 65 Ma extinctions,” she said.
The back-and-forth between scientists is vital to the scientific process, Gulick and Christeson said.
“There will be the cases where the minority is correct about a particular hypothesis and its a real battle to convince the majority that they are incorrect,” Gulick said.
He and Christeson cited plate tectonics as examples of a theory that was laughed out of the room—until the evidence became rock solid.
“The plate tectonics hypothesis was dismissed at first (one early paper was rejected with the suggestion that it was more suitable for conversation at a cocktail party than for publication in a scientific journal), but this now forms the foundation for all of earth sciences,” Christeson said.
And, it took a while for the dinosaur-killing asteroid theory to prevail.
Walter Alvarez, one of the scientists behind the theory, wrote a book about it called, “T. rex and the Crater of Doom.”
While the title might give it the air of an old-time Saturday matinee, the book is a good look at how Alvarez and his colleagues did the science and built the theory from the ground up.
The book details how the team travelled around the world collecting evidence and used an array of scientific instruments to analyze it. It took years, but the evidence convinced most of the skeptics.
And that’s what does the convincing scientists, Gulick said, “Hard scientific evidence.”
(Then there’s cartoonist Gary Larson’s “Far Side” explanation of the dinosaurs’ doom: A cartoon shows three dinosaurs lighting up and smoking cigarettes with the caption, “The real reason dinosaurs went extinct.”)
Gulick said the Chicxulub saga points out a problem that media have with reporting on science.
Too often, he said, reporters present two sides of a story as if each has comparable weight, even when one side is a small minority. This happens in reports about Chicxulub, climate change and evolution.
“The media is not doing their job unless the public gets the picture of how strong the evidence really is for something rather than always highlighting the debate regardless of how much scientific evidence exists on one side vs. the other,” Gulick said.
His suggestion: “Lets move on the next interesting questions. For Chicxulub, for instance, questions of how life rebounded from the impact, what were the exact killing mechanisms of the impact, and what are mechanics of forming a large impact crater in the Earth’s crust are all interesting scientifically.”
You’ll get no argument here.
Next: Chris Kirk, a physical anthropology professor, talks about taking on Darwinius masillae, the fossil billed as the oldest link in the chain of human evolution.